1. Field of the Invention
The present invention relates to audio amplifiers wherein improved means have been provided for reducing idling current, insuring stability, minimizing distortion and hum. The invention also relates to the integrated circuit (IC) fabrication of such amplifiers, wherein increasing complexity on the "chip" and decreasing complexity off the chip is favored, together with a minimum pin count.
2. Description of the Prior Art
Audio amplifiers have been fabricated for some time using solid state elements. With the advent of integrated circuits, the use of discrete transistors has tended to decline.
Once a decision to integrate has occurred, then fresh considerations obtain. Normally, integration should go as near to completion as possible. By comparison, outboarded components are more expensive and requiring additional pads which are also expensive should be minimized. Feedback loops, if possible, should remain on the chip to minimize both outboarded components and the pad count. Since the package tends to have a restricted heat dissipation capability any reduction in average dissipation will permit the amplifier to produce greater peak output signals. In addition, since many integrated circuit devices now find their way into battery operated devices, any reduction in average dissipation will substantially extend battery life.
In addition to the foregoing objectives having more direct application to integrated circuit considerations, the amplifier should have the usual performance requirements of high stability irrespective of the nature of the load presented by the loudspeaker, low distortion, low hum and adequate sensitivity to be driven by customary sources of audio signals. Such sources in most frequency usage are of course the detectors of AM-FM receivers and ceramic cartridges.
Integrated audio amplifiers are presently available. When operating at about a watt peak output, they normally use push-pull output stages, and degenerative feedback for assorted purposes. Most that are known, however, have reached a less than optimum solution to the other objectives herein outlined.